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Ultrathin PV Device is Highly Efficient

Photonics SpectraMar 2014
VALENCIA, Spain, & LAUSANNE, Switzerland, Dec. 30, 2013 — A thin film of perovskite sandwiched between two very thin organic semiconductors makes for a photovoltaic device with high power conversion efficiency, researchers have discovered.

The thin-film photovoltaic device.
A group led by Hendrik Bolink of the Instituto de Ciència Molecular (ICMol) at the University of Valencia developed the device in collaboration with colleagues at École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. The solar cells developed at ICMol were prepared using low-temperature processes similar to those used in the printing industry, Bolink said. The resulting hybrid organic-inorganic perovskite device is less than half a micron thick and can be prepared easily and inexpensively.

Currently, 85 percent of solar cells in use are based on crystalline silicon, while the rest use polycrystalline thin-film cells, mostly cadmium telluride/cadmium sulfide. These thin-film cells are cheaper to produce, but are based on rare and toxic elements. Methylammonium lead halide perovskites were recently identified as promising for solar cells, and over the past three years their performance has improved rapidly to reach efficiencies as high as 15 percent, the researchers said.

All previous high-efficiency perovskite solar cells used a mesoscopic metal oxide that requires a high-temperature sintering process, but Bolink’s group showed that sandwiching methylammonium lead iodide perovskite layers between two thin organic charge-transporting layers using room-temperature fabrication processes can also result in solar cells with high power-conversion efficiencies.

The research team.
It’s also possible to make the thin, lightweight devices semitransparent, which could allow them to be integrated into building facades, the researchers said. That way a building’s interior can be protected from intense sunlight by the solar cells while electricity is generated at the same time.

“We believe that this new class of perovskite solar cell using organic semiconductors to collect the charges will find widespread applications to rival photovoltaic solar cells based on thin films,” the team wrote in its paper, published in Nature Photonics. (doi: 10.1038/nphoton.2013.341)

A device for converting sunlight into electrical energy, consisting of a sandwich of P-type and N-type semiconducting wafers. A photon with sufficient energy striking the cell can dislodge an electron from an atom near the interface of the two crystal types. Electrons released in this way, collected at an electrode, can constitute an electrical current.